Ripening of viscose sirup



GGGGGGGGG ER RIPENING op vscosn SIRUP Patented Dec. 11, 1934 UNITEDsTA"1513s ,P..,ef'lla.NT oFFICE A RIPEN'ING 0F -VISCOSE' SIRUP A GeorgeA. Richter, Berlin,v H., assignor to Brown Company, of Maine BerIin, N.H... Aa corporation Application September2c5,1930, Serial No. 484,292 8Claims; (o1. eso-10o) This invention relates to a process of ripening ormaturing viscose sirup more particularly from the standpoint ofattaining that physicaly and chemical condition in the Sirup at which itis ready and satisfactory for spinning into artificial silk filaments. i

When cellulose xanthate is dissolved in-caustic soda solution to formviscose sirup so-called, theV fresh orunripenedA sirup cannotsuccessfully bel spun into the usual acid-setting baths for the reasonthat cellulose is'not regenerated from the xanthate to a suflicientextent and at the proper rate to give rise to filaments of thefdesiredtenacity, strength, elasticity, and other characteristics.

AIn order to realize these desiderata, it has beenv found necessary tosubject the viscose sirup to what is known as a ripening operation,during which operation it is generally understood that combined sulphursplits off and the cellulose complex becomes progressively poorer insulphur.

The ripening is carried toa point short'of gelling of the sirup, forwere gelling to take place, it would be impossible to handle the gel inthe usual' spinning: Y. machines without serious gumming vand pluggingof the pipe lines, pumps, spinnerets, and

other parts. The customary practice inproducing satisfactorily spinnableviscose sirups is to form a cellulose xanthate'solution in caustic sodacontaining '1% cellulose, calculated as cellulose but cessful spinning.Depending upon the nature of the fresh or unripened Sirup, it usuallytakes rfrom about 72 to 96 hours standing at 20 C. to produce a fullyand satisfactorily ripened Sirup.

'There arev many'disadvantages inherent in a viscose-ripening proceduresuch as hereinbefore described. Thusfthe equipment required is expensiveand occupies much space, including as it does a specialthermal-insulated room,"an elaborate system of refrigeration, controlof! the atof three to four days isexperienced'lbeforef'thesome hourswithout danger of gelling. itmay be desirable to cool the heat-ripenedsirup inventory'is adjustedto catch up with the demand of the spinningmachines, assuming that the plant is oneequipped with the number ofspinning machines to consume vthe entire output of theripeningapparatus. l

I have discovered that `the time knecessary for ripening viscoser sirupmay be reduced to a cornparatively negligible period, if the fresh orunripened sirup is heated to a temperature materially aboveknormal roomtemperature, say, to about 50 to 90 C. The particular temperature towhich the sirup is heated and the time period allotted for lheatingdepend on variousfactors, especially upon the` composition and thosecharacteristics of the sirup which determine its tendency to split offcombined sulphur and thereby to regenerate cellulose. For example, ifthe caustcity of the sirup is below normal, i. e., below 61/2%v causticsoda content, the" instability of the sirup is increased so that anelevated temperature at the low end of the rangegiven coupled with aperiod of heating of even one minute may suilce to produce the desiredripening effect.y On the other hand, other kinds of sirup may have to beheated for 15 minutes or more at the lowend of the temperature rangegiven before they reach the desired spinnable condition; and still otherkinds of sirup may have to be heated to temperatures as highas 90 C., oreven higher, at which temperatures, however, it is usually the case thatthe desired ripening action takes place quite rapidly. In any event,however, it is essential that 'the heat-ripened sirup either ybe chilledquickly to'temp'eratures downwards of 20 C. or

Q be spun practically as quickly as it is ripened in order tov avoid thegelling attendant upon keeping the heated Sirup inv ripened conditionfor a substantialperiod `oftime. VIn actual commercial i operation,it'may be more expedient to chill they sirup to downwards of 20 yC., asat such temperature it may be allowed to stand as a batch for In fact,

to as low as `10 C ,atwhich temperature it may be preservedfor dayswithout appreciable change, whereas 'abatchoi ripened sirup at'22o C.must be spun within about iive to six hours in order to avoidnon-uniformity of the artificial silk spun therefrom by reason of thefact that/the last porj batchl `When the sirup is of unusually highviscosity so that it may be spun only with diiculty at temperaturesdownwards of ,20 C., itis dis` tinctly advantageous tovs'pin the`heat-ripenedf tions of the batch have undergone spontaneous *50variation from the first portions of the same` Sirup in a hot"conditionimmediately as it is produced, as the hot Sirup is of low solutionviscosity and so lends itself to ready spinning. The normal sirups,however, even when at temperatures as low as 10 C., not only spinsatisfactorily but generally yield a better quality of silk at 10Wtemperatures because regeneration of cellulose is accompanied by lessviolent liberation of hydrogen sulphide4 which lat hightemperaturestends to occlude to the nascent silk filaments and to break them. Ifdesired, however, the heat-ripenedAlk Sirup may initially be chilled tothe desired ternperature whereat it may be kept stable, and the. coldSirup then heated to the desired temperature and viscosity immediatelybefore spinning. Such heating promotes lowering of solution viscosity,

which, as already indicated, is markedly affected by temperature change.

The principles of the present inventionA are applicable to a two-stageripening process in which the i'irst'orv second( stage consists inpermitting the Sirup to` ripen from, say, 12 to 24 hours, under theusual conditions. For instance, the fresh, unripened Sirup may be rstpartially ripened in the usual manner at 20C. over a 12` `.to effect theremoval of air orogas entrapped therein.' A two-stage ripening process,such as described, lends itself to practice with a temperature ofheating of the*v viscose Sirup; lower-thanthat necessary when` heatingalone is relied upon to accomplish allthe ripening of the Sirup.. Such.

a lower temperature of Aheating of the Sirup is desirable in that itleadsI to a ripened Sirup of better quality in thosev instances when theSirup.v

being handled iis"sensitive to a higher temperature With these and otherfeatures and objects in View, theprocess of the present invention willnowl be described with reference to the, accompanying drawing whichillustratesmore or` less diagram-l matically and conventionally one formof apparatus which may be employed for carrying out the process. y

Referring now in detail to the drawing, 1- rep-` resents' a'closed tankinto which the fresh, or unripened Sirup may be delivered by` a; pipe 2from` the filter press.v vThe pipe 2 may beA provided with a valve 3 sothat after lthe batch of Sirup has been discharged into the tank, the

valve may be closed to cut 01T flow ofsirupinto' the tankQ Passingthrough the top of thetank is a pipe 4 which conductscompressed airfrom,

an air-compressor or compressed air chamber; (not shown)y to theair-space above kthe batch of Sirup in the tank. The compressed airserves. to drive the Sirup through a pipe 5V extending from the bottomvof the tank upwardly through its top to a metering pump 6,-for instanceof the gear or piston type, which forcesV the sirupv at predeterminedcontrolled rate through a suitable;

heating System. The pipe 4 is preferably equipped with a valve 'lso thatthe air may be turned ofwhen the tank is being supplied with-a bath ofSirup and turned on when the pump isputin` operation to feed Sirupthrough the` Aheatingsyse tem.\ kThe kheating system may comprise`a;c,oil

8 within a jacketed tank 9, through the jacket 10 of which a suitableheating medium, Such as water or oil, may be circulated at a ratedesigned to heat the Sirup to the desired elevated temperature. Theheating medium may be Withdrawn from an upper side wall of the jacketthrough a pipe 11 into a heater 12 in which the medium receives heatfrom a steam coil 13, whereupon the heated medium may be Withdrawn fromthe heater by a pump 14 and passed through a pipe 15 into the bottom ofthe jacket. In order to control the temperature of the heating medium.so as to ensure heating of the Sirup tothe desired temperature, athermostat 17 may be providedin the tank 9 or in the pipe 16, whichconducts theheated'` sirup from the coil 8, the thermostat controllingthe opening or closing of a'ivalve 18 in the pipe 19 which suppliessteam to the steam coil 13. A normal unripened Sirup at an initialtemperature of 20 C. need remain in the coil 8; for only about fourminutes and be heated to a final temperature of about 75 C. to acquire afully ripenedl condition for spinning. If desired, thehot, ripened Sirupmay be ltered, asin such condition it. is very fluid and lends itself toilow through iiltering media. much more easily than sirups` at roomtemperature or lower. The lter is preferably of a design permitting thepresence of only a small volume of Sirup in the lter atany time so as toavoidI stagnation atany point in the filter, since, when theseconditionsare notv fullled, there is liable to be gelling o f the Sirup.

The ripened Sirup in heated condition may be delivered. to the spinningmachines and spun in such condition as previously described; and thismode of operation, is of advantage whenA a Sirup of high viscosity isemployed or when it is highly viscousbecause of a higher than the usual612% cellulose concentraton, I do not, however, herein claim per se thestep of spinning a hot viscose Sirup aslthis is disclosed in my Patent#1,678,- 354,issued July 24, 1928. According to the proces s of thatpatent, a highly viscous Sirupwhich has been ripened over a long periodin accordancewith, the prior art practiceisheated while it is on: itsway to the spinnerets, inV which case the viscosity of the Sirup isvastly reduced, but the time during which the sirupis hot is so shortastoA havefno appreciable ripening effect on the already ripened Sirup.The process of the present invention is differentiated from that of mypatent in that my present process involves the use, of an unripenedSirup as the raw.l material andtheheating of` the. Sirup to cause thisripening while at thesame timepermitting one to enjoy the benefit ofythe reduced viscosity. of the 4heated Sirup for spinning purposes, whensuch benefitis to be had. Ordinarily, however, it is preferable,aspreviously indicated, tocoolthe heat-ripened sirupto ,a temperature.downwards of 20 C., Say; to 10,v C., before the sirup-isspun.

o Accordingly, as depicted-inthe drawing, the heatwhich serves tomaintain the coolingy medium.

at the` desiredk low temperature. Thechilledsirup delivered fromv thecoolingcoil 8a. through the 21, from which. itA may bewithdravvnasneeded the spinning p machines.

Apipe- 20 .may be discharged'into-a storage tank.:

Another advantage in chilling the sirup before spinning is that I amenabled by my process to ripen sirups which have a strong tendencytoward gelling in ripened, hot condition, as is the case with viscoussirups having a lower than normal causticity. By chilling suchheat-ripened sirups to low temperatures, it is possible to check thegelling tendency sufficiently so that there is no danger of sirupspoilage. It is thus possible when applying the principles of thepresent invention to economize in the use of caustic soda` by producingunripened sirups of less than the `normal 61/2% caustic soda content andfurther to economize in the use of acid in the setting baths, as acid isconsumed by reaction with the caustic soda. Still another advantage inchilling the heat-ripened sirup flows from the fact that ripening byheat may be overdone without fear of spoiling the sirup by gelling, asthe quick chilling of an over-ripened sirup inhibits gelling tendenciessuiiciently long to permit spinning. It is of advantage to over-ripenthe sirup in certain instances, as I have found that by mixing orblending an unripened sirup with an over-ripened sirup, it is possibleto spin Silks having characteristics, diffcultly, if at all, attainableotherwise. Thus it is possible to produce silks having higher strengththan that of silk derived from a ripened or over-ripened sirup, andhaving softness far more pronounced than that of silk deriVed from anunder-ripened or unripened sirup. This combination of high strength andsoftness is doubtless attributable to the fact that an overripened sirupusually yields silk filaments of low strength but of high softness,whereas an underripened sirup usually yields harsh silk filaments ofhigh strength. By properly mixing or blending an over-ripened sirup withan under-ripened or unripened sirup, it is possible to realize acombination of both high strength and softness in the silk derived fromthe mixture.

What I claim is:

1. A process which comprises heating an unripened viscose sirup to aripened condition short of gelling, and indirectly cooling theheat-ripened sirup quickly and artificially to a temperature at whichthe sirup may be kept `in ungelled condition for a considerable periodof time.

2. Aprocess which comprises maintaining an unripened viscose sirup attemperatures of from 50 to 90 C. for a relatively short period of timeto ripen it short of gelling, and indirectly and quickly .cooling theheat-ripened sirup artificially to downwards of 20 C. to avoid gellingupon standing of the sirup.

3. A process which comprises progressively withdrawing unripened viscosesirup in controlled amount as a stream from a bulk supply, indirectlyand quickly heating the stream to a ripened condition short of gelling,and then indirectly and quickly cooling the stream artificially to atemperature at which the ripened sirup may be kept in ungelled conditionfor a considerable period of time.

4. A process which comprises progressively withdrawing unripened viscoseSirup in controlled amount as a stream from a bulk supply, indirectlyand quickly heating the stream to a ripened condition short of gelling,and then indirectly and quickly cooling the stream artificially todownwards of 20 C.v to check gelling tendencies therein.

5. A process which comprises progressively withdrawing unripened viscosesirup in controlled amount as a stream from a bulk supply,

indirectly and quickly heating the stream to a temperature of about 50to 90 C. and maintaining such temperature for about 1 to 15 minutes toripen the sirup short of gelling, and then indirectly and quicklycooling the stream artificially to about -to 10 C. to check gellingtendencies therein.

6. A process which comprises progressively withdrawing unripened viscosesirup in controlled amount as a stream from a bulk supply, indirectlyand quickly heating the stream to a ripened condition short of gelling,filtering the stream, and then indirectly and quickly cooling the streamartificially to a temperature at which the ripened sirup may be kept inungelled condition for a considerable period of time.

7. A Aprocess which comprises indirectly heating an unripened viscose toa ripened condition short of gelling, and indirectly cooling theheatripened sirup quickly and artificially to a temperature at which thesirup may be kept in ungelled condition for a considerable period oftime.

8. A process which comprises indirectly heating an unripened viscosesirup to a temperature of about 50 to 90 C. and maintaining it at suchtemperature for a short period of time to ripen it short of gelling, andindirectly and quickly cooling the heat-ripened sirup artificially todownwards of 20 C. to avoid gelling upon standing of the sirup.

GEORGE A. RICHTER.

